Selective catalytic reduction exhaust aftertreatment systems are an important technology for reducing harmful emissions from internal combustion engines. Selective catalytic reduction catalyst aftertreatment systems generally include a source of storage for reductant (particularly diesel exhaust fluid) and a dosing unit that includes at least one of a pump unit for pressurizing the reductant. The selective catalytic reduction catalyst aftertreatment systems may also include a metering unit for providing a controlled amount or rate of reductant and an injector, which provides a reductant solution to a decomposition region of an exhaust flow path located upstream of a selective catalytic reduction catalyst. Some selective catalytic reduction catalyst aftertreatment systems also utilize pressurized gas to assist the flow of reductant to the injector.
While being useful in reducing nitrogen oxide emissions, selective catalytic reduction catalyst systems may suffer from a number of shortcomings. For example, the reductant injected into the exhaust flow may not properly mix with the exhaust flow exiting an engine. In some instances, the reductant can puddle along an inner wall of the exhaust system, forming a deposit over time.